1. Field of the Invention
This invention relates to catalysis, and particularly to hydrocarbon hydroprocessing catalysts, such as those utilized to catalyze the reaction of hydrogen with organosulfur, organonitrogen, and organometallic compounds. More particularly, this invention is directed to catalysts and a method for preparing catalysts for hydrodesulfurizing hydrocarbon liquids.
Residual petroleum oil fractions, such as the heavy fractions produced in atmospheric and vacuum crude distillation columns, are usually undesirable as feedstocks for most refining processes due to their high metals and sulfur content. Economic considerations have recently provided new incentives for catalytically converting the heavy fractions to more marketable products. However, the presence of high concentrations of sulfur and metals, the latter often being found in relatively large porphyrin molecules, precludes the effective use of residua as feedstocks for cracking, hydrocracking, and similar catalytic refining operations.
Methods are available to reduce the sulfur and metals content of residua. One such method is hydrodesulfurization, a process wherein a residuum, usually containing the bulk of the asphaltene components of the original crude from which the residuum was derived, is contacted with a catalyst under conditions of elevated temperature and pressure and in the presence of hydrogen, such that the sulfur components are converted to hydrogen sulfide while the metals are simultaneously deposited on the catalyst.
The typical hydrodesulfurization catalyst is composed of Group VIII and Group VIB components, such as cobalt and/or nickel plus molybdenum components, on a porous refractory oxide support, but it may also contain other components. For example, U.S. Pat. Nos. 3,968,026 through 3,968,029 disclose titanium-promoted alumina supports as highly effective in catalysts promoting desulfurization.
It has also been recognized that catalysts having specific pore size distributions and/or surface area characteristics are effective for hydrodesulfurization purposes. For example, U.S. Pat. Nos. 4,082,695, and 4,089,774 describe processes for removing metals and sulfur from residua utilizing catalysts having specific pore size distributions.
Several methods are known in the prior art to improve the porosity characteristics of support particles used in catalysts. One such method, disclosed in U.S. Pat. No. 2,890,162, involves impregnating a porous starting material with a molybdenum and/or cobalt metal component that serves as a pore size distribution growth promoter. Other methods involve incorporating certain liquids or phosphorus in the catalyst preparation materials, as note U.S. Pat. Nos. 4,022,715 and 4,003,828, respectively. However, these and other methods provided only limited improvements before other desirable characteristics are adversely affected, and a need still exists for alternative methods of producing catalysts and catalyst supports used in hydrorefining processes.
It is, therefore, a major object of the present invention to provide a method for producing hydroprocessing catalysts of improved characteristics, and specifically, to provide a method resulting in a catalyst having a predetermined, beneficial electronegativity for the particular hydrorefining process in which the catalyst will be utilized.
It is another object of the invention to produce catalysts and/or catalyst supports characterized by a predetermined geometric mean electronegativity value.
It is a further object of this invention to provide a method using electropositive and/or electronegative components to control the geometric mean electronegativity value of catalyst supports comprising porous refractory oxide particles, and, optionally, to improve the physical characteristics thereof, as by increasing the average pore diameter or decreasing the surface area, or both.
Another object is to produce improved catalysts and/or catalyst supports by employing, during the preparation of said catalysts or supports, electronegative and/or electro-positive elements that function not only as agents affecting the geometric mean electronegativity of the catalyst or support but also as pore growth promoters, which, in the preferred embodiment, provide for a substantially larger average pore diameter than would be possible if the catalyst or support were prepared under similar conditions but in the absence of said electronegative and/or electropositive element.
Another object is to provide a method for substantially altering the physical and chemical properties of precalcined gamma alumina particles without causing substantial phase transformation to other forms of alumina.
Still another object is to provide a hydrorefining process, and most particularly a hydrodesulfurization process, using catalysts having predetermined geometric mean electro-negativity values, or catalysts having supports characterized by predetermined geometric mean electronegativity values. These and other objects and advantages of the invention will become apparent from the following description.